Which of the following order is/are correct?

Options

A. `Mg^(2+)("size") gt Li^(+)` (size)
B. `S(E.A)gtO(E.A)`
C. `Hg(I.E.) gt Cd(I.E)`
D. `P(I.E) gt S(I.E)`

Answer

To solve the question regarding the correct order of various properties, we will analyze each statement provided in the question one by one.

### Step 1: Analyze the first statement
**Statement:** Magnesium ion size is greater than lithium ion size.

**Analysis:**
- The ionic size generally decreases across a period due to increasing nuclear charge, which pulls the electrons closer to the nucleus.
- Magnesium (Mg) is in Group 2 and Lithium (Li) is in Group 1.
- Both Mg and Li form cations (Mg²⁺ and Li⁺). However, Mg²⁺ has a higher positive charge than Li⁺, which means that Mg²⁺ will have a smaller size due to stronger attraction of electrons to the nucleus.
- Therefore, this statement is **incorrect**.

### Step 2: Analyze the second statement
**Statement:** Sulfur electron affinity is greater than oxygen electron affinity.

**Analysis:**
- Electron affinity is the energy change when an electron is added to a neutral atom.
- Oxygen has a smaller atomic radius than sulfur, and with more electrons in the valence shell, the added electron experiences significant electron-electron repulsion.
- In sulfur, the larger atomic size leads to less repulsion when an electron is added.
- Hence, the electron affinity of sulfur is indeed greater than that of oxygen, making this statement **correct**.

### Step 3: Analyze the third statement
**Statement:** Mercury ionization energy is greater than cadmium ionization energy.

**Analysis:**
- Ionization energy generally increases across a period and decreases down a group.
- Mercury (Hg) is in Group 12 and Cadmium (Cd) is also in Group 12 but is above mercury in the periodic table.
- Due to the presence of d-electrons and relativistic effects, mercury has a lower ionization energy compared to cadmium.
- Therefore, this statement is **incorrect**.

### Step 4: Analyze the fourth statement
**Statement:** Phosphorus ionization energy is greater than sulfur ionization energy.

**Analysis:**
- Ionization energy generally increases across a period due to decreasing atomic size.
- However, phosphorus has a half-filled p-orbital configuration (3p³), which is more stable and requires more energy to remove an electron compared to sulfur (3p⁴).
- Hence, the ionization energy of phosphorus is indeed greater than that of sulfur, making this statement **correct**.

### Conclusion
Based on the analysis:
- The correct statements are:
- Statement 2: Sulfur electron affinity is greater than oxygen electron affinity (Correct)
- Statement 4: Phosphorus ionization energy is greater than sulfur ionization energy (Correct)

The incorrect statements are:
- Statement 1: Magnesium ion size is greater than lithium ion size (Incorrect)
- Statement 3: Mercury ionization energy is greater than cadmium ionization energy (Incorrect)

### Final Answer:
The correct orders are statements 2 and 4.

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